Narcoblixes

A species of Blix, they have the power to enter a trance and control the bodies of those people they have bitten, but only if those people are asleep. Vanessa Santoro, a major character in book 2, is a Narcoblix who bit the other characters in their sleep in an attempt to steal one of the five artifacts and overthrow the preserve. She was thwarted and put into the QuietBox to keep her from controlling those she had bitten. In book 4, Vanessa told Kendra that as her mind was resistant to mind control, she could not control her in her sleep despite having bitten her. This implicates that Narcoblixes use a kind of mind control to control people in their sleep.
Wayn was another Narcoblix introduced in book 5.
Later in the same book, Vanessa and Bracken have a slight unicorn vs. blix rivalry, possibly meaning that the two species do not get along very well.